1. Field of the Invention
The present invention relates to a heat exchanger, and more particularly, to a heat exchanger that is designed to effectively guide air flowing along fins disposed between tubes up to rear ends of the tubes.
2. Description of the Related Art
Generally, a heat exchanger is installed in an air conditioner and functions as an evaporator or a condenser for performing a heat exchange between a refrigerant and air. A fin-tube type heat exchanger is widely used among various kinds of the heat exchanger.
In the fin-tube type heat exchanger, the fins installed in a tube for air flow are classified into a slit fin, a louver fin, and a corrugate fin that is formed in a W-shape.
FIG. 1 shows a conventional heat exchanger having the corrugate fin.
Referring to FIG. 1, a heat exchanger 1 includes a plurality of corrugate fins 10 spaced away from each other at a predetermined distance and formed in a W-shape, and a plurality of tubes 30 disposed penetrating the corrugate fins 10 at right angles and along which a refrigerant flows.
Here the fin 10 is provided with peak portions 12 and valley portions 14 at which the tubes are not penetrated and which are intersected with each other at a predetermined angle, a plurality of fin collars 16 defining tube insertion holes through which the tubes are inserted, and a plurality of seats 18 formed in a concentric circle shape to support the fin collars 16.
Herein, the conventional heat exchanger having the corrugate fin will be described with reference to FIGS. 1 to 4.
Referring to FIG. 1, the heat exchanger 1 is a fin-tube type, and a plurality of fins 10 and a plurality of tubes are intersected with each other in a perpendicular direction. The tubes 30 arranged in two rows penetrate the plurality of fins 10 in a perpendicular direction.
Each of the fins 10 is the corrugate fin (hereinafter, abbreviated a fin). Each of the fins 10 has a plurality of donut-shaped flat portions and a plurality of inclined portions that are defined by the W-shape having a plurality of the peak and valley portions. The fins 10 are installed on the tubes 30 in a longitudinal direction of the tubes 30, being spaced away from each other at a predetermined distance.
Referring to FIGS. 2 and 3, there is shown a detailed structure of the fin 10. The fin 10 is formed in a W-shape with the peak and valley portions 12 and 14 that are alternately formed. That is, the fin 10 has two side ends that are respectively defined by the valley portions 14a and 14c. In case a plurality of fins 10 are used, the tubes 30 are arranged in two rows in a zigzag-shape in order to improve a heat exchange efficiency.
That is, each of the fins 10 installed on the tube 30 has two peak portions 12a and 12b and three valley portions 14a, 14b and 14c, which are alternately disposed and connected by inclined surfaces. The shape of the fin 10 is symmetrical based on the longitudinal valley portion 14b. Central axes of the zigzag-shaped tube 30 pass through the longitudinal center valley portion 14b. 
The fin 10 is provided with a plurality of tube insertion holes 16a, central axes of which correspond to the respective central axes of the zigzag-shaped tube 30. The fin collars 16 are elevated from the fin 10 to define the tube insertion holes 16a through which the zigzag-shaped tube 30 is inserted. The tube 30 surface-contacts an inner circumference of each collars 16.
The seat 18 is formed in a concentric circle shape around a lower end of an outer circumference of the fin collar 16 to support the fin collar 16 and to allow air to flow in the form of enclosing the tube 30 and the fin collar 16.
An inclined portion 20 is formed on the fin 20 around the seat 18 to prevent the air flowing around the tube 30 from getting out of a circumference of the tube 30. The inclined portion 20 is inclined upward from the seat 18 to the adjacent peak portions 12.
The seat 18 is located on a horizontal level identical to that where the valley portions 14 are located. Heights and depths H1 and H2 of the peak and valley portions 12 and 14 are identical to each other. That is, the H1 indicates the heights of the adjacent peak portion 12 from the valley portions 14, and the H2 indicates the depths of the adjacent valley portion 14 from the peak portion 12. In addition, the inclined surfaces connecting the valley portions to the peak portions are inclined at an identical angle (θ).
FIGS. 4(a) and 4(b) are respectively front and rear views of the fin, in which the peak portions 12 and valley portions 14 depicted in FIG. 4(a) correspond to the valley portions 14 and peak portions 12 depicted in FIG. 4(b), respectively.
When the air is introduced into the heat exchanger 1, the growth of a frost formed on an outer surface of the fin 10 is proportional to an amount of a heat transfer on the outer surface of the fin 10. At this point, the air flow speed is increased at the tube area as well as at the fin areas between the tubes 30 disposed in a longitudinal direction, thereby forming a high-speed air flow. As a result, the heat transfer coefficient is increased and the frost layer is quickly grown on the surface of the fin 10.
In case the frost layer is grown on the surface of the fin 10, since the distance between the adjacent fins 10 is reduced, an air passage area is also reduced. Due to the reduced area, the air flow speed is increased much more. As a result, the pressure drop of the air is increased in a parabola shape as time passes. Further, the heat transfer amount of the heat exchanger is also greatly reduced.